A vehicular exhaust system comprises one or more pipes for carrying exhaust gases from the engine. Each pipe extending from the engine may lead to a catalytic converter which is operative to convert certain objectionable gases in the exhaust stream into less objectionable forms. An exhaust pipe extends from the catalytic converter to a muffler which is operative to attenuate the noise associated with flow of exhaust gases. A tail pipe then extends from the muffler to a location on the vehicle where the exhaust gases can be safely and conveniently released.
The typical prior art exhaust muffler comprises a plurality of separate tubes supported in a parallel array by a plurality of transversely extending baffles. Selected portions of each tube may comprise perforations, louvers or apertures to permit exhaust gases traveling therethrough to escape in a controlled manner. Each tube typically is securely connected to at least one baffle and the array of assembled parallel tubes and transverse baffles are then slid into a generally tubular shell having a circular or oval cross-sectional configuration which corresponds to the shape of the baffles. A separate outer wrapper typically is wrapped around the outer shell to dampen noise associated with the vibration of the shell. A pair of opposed end caps or headers are then securely connected to the opposed longitudinal ends of the tubular shell and outer wrapper to substantially enclose the muffler. Each end cap typically comprises at least one aperture to permit communication with the internal portions of the muffler. The apertures in the end caps typically are aligned to mate with one of the tubes within the muffler. The assembly of components in this typical prior art muffler defines a plurality of chambers. In particular, chambers are defined between the tubular shell and either a pair of spaced apart baffles or between one baffle and one end cap of the prior art muffler. The relative spacing of the baffles in the muffler, the dimensions of the tubes therein and the dimensions of the perforations, louvers, apertures or the like are all selected to enable a specified attenuation of exhaust gas noise. More particularly, the exhaust gas flowing through the system expands through the various perforations, louvers, apertures or the like and into the corresponding chambers to achieve the specified noise attenuation.
When the above described exhaust muffler is intended for an original equipment installation, the muffler typically is welded to the elongated circuitous exhaust pipe and tail pipe. The assembly of the muffler, the exhaust pipe and the tail pipe is then delivered to the original equipment vehicle manufacturer, such that the complete exhaust system assembly can be mounted to the vehicle.
The prior art mufflers and exhaust system components described above generally have provided adequate attenuation of noise associated with the flow of exhaust gas. However, the prior art exhaust muffler has required a large number of separate components which had to be assembled in a labor intensive manufacturing process. The resulting muffler tended to be unnecessarily heavy and offered few design options pertaining to the shape of the muffler or the alignment of pipes leading to or away from the muffler. These inherent limitations with the above described prior art mufflers have made it extremely difficult to fit the exhaust system into the limited available space on the underside of the vehicle.
The prior art further includes mufflers which comprise stamp formed components. For example, U.S. Pat. No. 4,396,090 which issued to Wolfhugel on Aug. 2, 1983 shows a muffler having a pair of internal plates stamp formed to define pairs of opposed channels. The internal plates are assembled such that the channels are in register with one another and define tubes therebetween. The internal plates are then disposed within the above described conventional wrapped outer shell to define a muffler. Separate internal baffles extend between the stamped plates and the wrapped outer shell to define chambers within the muffler of U.S. Pat. No. 4,396,090.
The prior art also includes mufflers consisting of only two opposed shells which are stamped to define a convoluted array of stamp formed tubes and stamp formed chambers. Mufflers of this type are shown in: U.S. Pat. No. 2,484,827 which issued to Harley on Oct. 18, 1949; U.S. Pat. No. 3,176,791 which issued to Betts et al. on Apr. 6, 1965 and U.S. Pat. No. 3,638,756 which issued to Thiele on Feb. 1, 1972.
The prior art further includes mufflers that are formed from four stamped components. Mufflers of this type comprise a pair of internal plates that are stamped to define opposed channels. The plates are secured in face-to-face relationship with one another such that tubes are defined by the opposed channels. The internal plates are further provided with stamp formed perforations, louvers or the like to permit expansion of the exhaust gas from the formed tubes. These mufflers further comprise a pair of stamp formed external shells which define a chamber surrounding and enclosing the internal plates. The chambers define a single enclosed volume into which the exhaust gases may expand. Prior art mufflers of this general type are shown in: British Patent No. 632,013 which issued to White in 1949; British Patent No. 1,012,463 which issued to Woolgar on Dec. 8, 1965; and U.S. Pat. No. 4,132,286 which issued to Hasui et al. on Jan. 2, 1979.
Certain prior art mufflers have been formed from three or more stamped components plus a plurality of tubular components. For example, the above cited U.S. Pat. No. 4,132,286 to Hasui shows a muffler having a perforated internal plate which is stamped to define at least one channel. Conventional tubular members conforming to the shape of the channels in the perforated plate are supported by and retained in the channels. The muffler of U.S. Pat. No. 4,132,286 further comprises a pair of opposed stamp formed external shells effectively defining a clam shell to surround the perforated internal plate and the tubes supported therein. The muffler shown in U.S. Pat. No. 4,132,286 effectively defines only a single internal chamber into which exhaust gases expand. The acoustical tuning capabilities of a muffler of this general type are very limited, and it would be extremely difficult for a muffler as shown in U.S. Pat. No. 4,132,286 to achieve the noise attenuation requirements of mufflers for most vehicles manufactured or sold in the United States.
A muffler similar to the muffler shown in the above cited U.S. Pat. No. 4,132,286 is shown in British Patent No. 2,120,318 which issued to Allday on Nov. 30, 1983. In particular, British Patent No. 2,120,318 shows a muffler having a plurality of tubes supported in a parallel array by a plurality of tranversely extending baffles. The array of tubes and the baffles are disposed in opposed stamp formed external shells of generally clam shell configuration. However, the external shells shown in British Patent No. 2,120,318 are part of extremely complex stampings which further define both a stamp formed exhaust pipe and a stamp formed tail pipe. The stamped external clam shells and the stamped exhaust pipe and tail pipe unitary therewith would require extremely expensive dies. Furthermore, the internal components required by British Patent No. 2,120,318 inherently require the combination of tubes and separate baffles which must be assembled in the labor intensive manufacturing processes described with respect to the traditional prior art muffler.
Still another prior art muffler incorporating both tubular and stamped components is shown in published Japanese patent application No. 59-43456. Unlike the two previously described references, the muffler shown in Japanese application No. 59-43456 includes at least four stamped components in combination with tubular members. In particular, the muffler shown in Japanese patent application No. 59-43456 includes a pair of stamped internal plates with formed channels that define tubes when the internal plates are disposed in face-to-face relationship. Additionally, portions of each internal plate are folded generally orthogonal to the remainder of the plates to define a wall extending transverse to the stamp formed tubes. Separate stamp formed baffles also are provided. The muffler shown in published Japanese patent application No. 59-43456 further comprises a pair of stamp formed exterior clam shells which surround the internal plates. The external clam shells and the folded portions of the internal plate define complementary configurations, such that the folded portions of the internal plates define baffles within the muffler. The muffler further includes tubular members which extend between the external shell and the baffles formed by the folded portions of the internal plates. The muffler shown in Japanese patent application No. 59-43456 is extremely complex, expensive and could be difficult to assemble. In particular, this muffler includes at least four stamped components with corresponding dedicated dies plus a pair of separate tubular members. It is believed that the stamped internal plates would have to be assembled and welded to one another. The separate tubular members would then have to be securely connected to the stamped internal plates by welding or the like. The separate baffles would also have to be securely connected to the stamped internal plates. The opposed exterior clam shells would then have to be securely assembled around the subassembly consisting of the opposed stamped internal plates, the separate baffles and the separate tubes.
The above described prior art stamp formed mufflers provide certain advantages over the conventional mufflers with wrapped outer shells. In particular, many of the above described stamp formed mufflers would be lighter than conventional mufflers and could be manufactured in processes that are well suited to automation. However, most of the above described prior art stamp formed mufflers generally did not provide a level of acoustical tuning that would be acceptable on vehicles manufactured or sold in the United States. As a result, until recently, stamp formed mufflers did not achieve significant commercial success in the United States.
Recently there have been several substantial advances in the stamp formed muffler art. In particular, U.S. Pat. No. 4,700,806 which issued to Jon Harwood on Oct. 20, 1987 shows a muffler formed from stamp formed components and providing the combination of at least one tuning tube and at least one low frequency resonating chamber. One embodiment of the mufflers shown in U.S. Pat. No. 4,700,806 shows a pair of internal plates formed to define channels therein. The plates are secured to one another such that arrays of tubes are defined by the channels. Selected portions of the channels are provided with perforations or other such aperture means for permitting a controlled expansion of the exhaust gases flowing through the formed tubes. The muffler of U.S. Pat. No. 4,700,806 further comprises a pair of external shells. In the above referenced embodiment, the external shells comprise a peripheral portion and a crease connecting spaced apart locations on the peripheral portions. The crease is formed to be in contact with the internal plate substantially continuously between the peripheral portions of the external shell. Thus, the crease shown in U.S. Pat. No. 4,700,806 effectively defines a baffle which enables a plurality of chambers to be defined by the external shell. The location of the crease shown in U.S. Pat. No. 4,700,806 is selected in accordance with the volume of the chambers required for the specified noise attenuation and exhaust gas flow characteristics.
Other improvements relating to stamp formed mufflers are shown in U.S. Pat. No. 4,736,817 which issued to Jon Harwood on Apr. 12, 1988; U.S. Pat. No. 4,759,423 which issued to Jon Harwood et al. on July 26, 1988; U.S. Pat. No. 4,760,894 which issued to Jon Harwood et al. on Aug. 2, 1988; and, U.S. Pat. No. 4,765,437 which issued to Jon Harwood et al. on Aug. 23, 1988. All of the above described Harwood patents are assigned to the assignee of the subject invention, and the disclosures thereof are incorporated herein by reference.
Mufflers manufactured in accordance with the above described Harwood patents have achieved considerable commercial success in a very short time. All of this commercial success relates to original equipment mufflers where the number of mufflers of a particular type have been sufficient to readily offset the costs associated with the stamping dies. It is anticipated, however, that there may be some situations where the volume of mufflers may be small, thereby increasing the per muffler costs associated with the four stamping dies required for four stamp formed components of a muffler. It is also anticipated that in some situations the exhaust gas flow will require fairly uncomplicated acoustical tuning. For these situations, it is desired to provide a muffler that can be manufactured with very low initial manufacturing costs and low material costs, while still providing the very desirable advantages of a manufacturing process that is well suited to automation. Furthermore, it is well known that weight reductions can improve fuel efficiency and other aspects of engine performance. Therefore, it is desirable to provide lower weight vehicular components whenever possible.
Accordingly, it is an object of the subject invention to provide an exhaust muffler having a substantially minimal number of components.
It is another object of the subject invention to provide a very light weight muffler and exhaust system.
An additional object of the subject invention is to provide a muffler with stamp formed components but with low die costs.
Still a further object of the subject invention is to provide a muffler which facilitates automated welding of the muffler components.
Another object of the subject invention is to provide a muffler with baffles of integral construction and unitary with the external shell for supporting tubular components of the muffler.